Venting and insulating ceiling

[AshurB]

I am in the middle of insulatating my attached garage. I have finished the walls and waiting on a kit for the door. Now to the ceiling, there is a soffit on the front and back of garage with a roof ridge vent. I would like to insulate the ceiling but due to blockers in the rafters I can't seem to find an answer on how I should go about it.

I understand it needs to be vented, so rafter vents or a baffle will have to be used. How do I go around the blockers and do I go all the way to the ridge vent with vent chutes. Not all the rafters have them.

 

[The Cobbler]

just staple the baffles to the underside of that blocking , then to the roof deck up higher. remember to dam the top of the wall to the baffle to , if you'r blowing it in
and the baffles just need to go higher than the insulation, not all the way to the ridge

 

[AshurB]

I will be putting in fiberglass insulation. Do I put baffles from the soffit to the ridge in every rafter?

 

[The Cobbler]

I would put baffles in each rafter cavity, but you don't need to go to the ridge, just higher than the insulation. if you're using batts, and you're careful not to block the bay, you can get by without baffles

 

[AshurB]

Ok the rafters are made of 2x6s if I were to use faced batts or rolls for 2x4s that should leave plenty of room above the insulation to get past the blockers

 

[The Cobbler]

ok, I see now, you don't have any ceiling rafters , you're insulating under the roof then?
so you will need a baffle in each bay to the ridge .
sorry

 

[AshurB]

That was my fear. Yes, I will be putting insulation right under the roof.

 

[The Cobbler]

I would staple the baffles to the underside of the roof deck & get creative where the blocking is , maybe turn a pc of baffle 90degrees on top of the ones under the deck to create a space

 

[AshurB]

I knew this wasn't a normal situation. I'll put baffles in every cavity to start then work on the ones without blockers. Save the blocked cavities for last.

 

[AshurB]

Would this be what I would need? I would just line it all the way up

www.amazon.com/AccuVent-Flame-Retar...dp/B01G2HVBVG/ref=sr_1_3?ie=UTF8&qid=15441559

 

[The Cobbler]

you probably don't need the flame retardant one,just the cheep styro ones will do but that's basically what you want

 

[AshurB]

Ok sounds good. Thank you.

 

[AshurB]

I've bought the foam insulation vents. They are 22". My rafters are 16"oc I dont see how I'm supposed to cut them to fit inside and still have it vented. If I cut along the perforation they are only 11".

 

[Stuart in MN]

There is a building technique referred to as a hot roof, where you don't include ventilation between the bottom of the roof itself and the insulation layer. You may want to investigate it to see if it's appropriate (or allowed) in your situation.

 

[AshurB]

I ended up putting up the rafter vent to the ridge. I was told I needed spacers but due to the wood blockers I didnt put in spacers in some. Is there a benefit for the 1" spacer?

 

[Chris705]

You’re going thru the pains of putting up the vents, so yes keep at it and add the baffles up to and beyond the “sheathing nailers” that the builder installed. You want to fabricate a path for hot air to pass up the baffle and get beyond the nailer. You could accomplish this by adding spacers on each end of the nailer and using 1/4” plywood or the more rigid plastic baffles. Or use rigid foam board to go over the nailer, still using a spacer. Then you can **** the fiberglass insulation to the rigid insulation. Stop the foam baffles about 1-1/2” from the nailer & run either your foam or plywood out over the foam baffles to lap the ends a few inches. That will create an air channel to continue a path for air to enter at a he soffit and exit at the ridge vent. Keeps the roof deck cooler than not providing an air path. Keeping your shingles from over cooking. Good luck.

 

[kngelv]

Man, I hate being the bearer of bad news but you have not installed those baffles correctly. The spacing that they are talking about is between the baffle and the underside of the roof sheathing - not between each baffle.The baffles have to be continuous from the soffit to the ridge vent.Two inches is better but one inch is the code minimum.You can just cut small sections of a baffle to cover the gaps.The sucky thing about this is the blockers are really going to restrict airflow in those channels. Also if you have 2x6 roof joists you can only fit R-19 in there which is not much in Michigan. R-45 is what you need. You also have to cover it with drywall or something. You might have insurance issues if you don't. I realize you probably want to have storage space up there which is why you are trying to insulate under the roof but is there any chance of covering the ceiling and insulating on top. The only shot of getting the right amount of insulation under there and doing it the way you want is by getting it covered with closed cell foam sprayed directly on the underside of the roof. Problem is it's not cheap. Good luck with all of this. BTW what part of Michigan are you in? I'm just south of Detroit.

James

 

[AshurB]

That makes sense. It shouldn't been to hard to cover the gaps. I'm not to worried about the r value. My main concern was stopping the air coming in from the soffit. With these vent I caused a small draft but I haven't put any baffles or blockers to stop the air from coming in and I'll put the 2x6 insulation in after.